Ambulatory children with cerebral palsy (CP) have diminished muscle power and rate of force production, which limits their walking activity and ability to physically participate in day to day life. Locomotor treadmill training (LTT) to enhance walking in children with CP has been shown to be no more effective than traditional rehabilitation strategies. The objective of this application is to determine the effect of short-bust interval LTT without body weight support on the primary outcomes of walking performance and capacity, and secondary outcome of daily participation in children with CP. To identify key muscular mechanisms with this type of training, we will examine quadriceps muscle performance and architecture. In addition, we will collect preliminary data on two LTT dosing schedules. The rationale for this proposed research is that short-burst interval LTT will enhance muscle power production and subsequently walking performance and capacity via training protocols that are motivating and mirror the walking and physical activity patterns of typically developing (TD) youth. We hypothesize that LTT strategies for children with CP modeled on activity patterns in TD children, rather than activity patterns of adults, will positively affect muscle power generation and subsequently improve community-based walking activity with a positive trend in participation. This hypothesis will be tested by the following specific aims. Aim #1: examine the effect of short-burst interval LTT on walking performance, capacity, and day-to-day participation in ambulatory children with CP. Short-burst interval LTT will consist of a 30-sec burst of high speed walking alternating with a 30-sec interval of slow to moderate speed walking, working towards a total of 30 minutes. Twelve ambulatory children, 6-12 years old with bilateral spastic CP will be enrolled. Sub-aim #1a: preliminary comparison of two dosing schedules of short-burst interval LTT. All participants will be randomized to one of two dosing schedules of 20 total sessions, 5x/week for 4 weeks or 2x/week for 10 weeks. Aim #2: quantify the effects of short-burst interval LTT on in vivo muscle architecture and muscle performance. Muscle architecture will be measured using ultrasound imaging and muscle power, strength, and rate of force development will be measured with isokinetic dynamometry. This project is innovative because it focuses on a unique approach for addressing walking limitations in children with CP and implements the StepWatch accelerometer for community-based walking activity outcomes. The proposed research is significant because it will be the first step in a continuum of research that is expected to direct locomotor training protocols and rehab strategies across pediatric disabilities and positively effect changes in community-based walking activity for children with CP. Advances in the understanding of the muscular mechanisms by which children with CP respond to high speed short-burst training are expected. Such knowledge also has relevance to the health and functional benefits of enhanced mobility and physical activity across the life span.